Trunk circuits



Dec;'26, 1922. 1,440,110. c. SPARKS.

mum cmcuns.

FILED APR. 4, 191B- 2 SHEETS-SHEET ln B s DUE/172017 Zhaglggjuar/rs.

m m M l PC K N CU R T Dec. 26, 1922.

2 SHEETS-SHEET 2.

FILED APR. 4,1938.

fin/E27 01-."

[harks HZYZvrzfs Patented Dec. 26, 1 922.

.omainns 52223115; or

CHICAGO, ILLDN'UIS. As'srem'aa no KELLOGG swncma'aimn AND SUPPLY onrmmnr CHICAGO, InLmo'I's, A CORPORATION OF ILLINOIS.

4 iiiiiiiic' CIRCUITS.

enfplo ei'aton n the ma over a think extending to the priva'te' brunt-h exchange on which the private branch eit-hantz'c operator has left. a cord circuit plug in a jack, the ringing current is disconnected from the private branch exchange cord cir- (-nit, thus preventing the private branch ex vhaneei operato'i" fr'dtn being rung in the ear and also prevents the ringing of the private hymn-h exchange subseribei"s bell connected in the private ln-un'ch exchange (-0111 r-ir- ('Hli.

still further feature is the prm'isi'm imzins for preventing the lighting: 0'? the 12:1.- il-nnp nssneiuted with a trunk leading: to the private ln'aneh ext-hung? when the main 0):- i-hauge operator z'enmves the calling! plug of a ((aili circuit from the outgoing jaek 0f tlnsaid trunk circuit before the private hrnueh change ngie'i'fitrii' hastake-n (iO'fi'll the litftllll. :1: the private hrnnr-h exvhange.

Qth'enbbjcts 0f iny invemidn will his ino're particularly pointedbht in 'the follqiw mg spcilication and in the ap'p'e'riiliiil claii'ns.

Befptfinginon"more in'tle tail to my inventiqn ns illlitia'td, I show in l a en'euit arxiinglnent in which the triin'k circui't of my inventibn is adapted to st'ahlis'h n corihbfioxnbetiv'en a calling sub's'ci'ihei of a m'ziinexcliange and a piivate bruii'ch exchan e subscriber. In 2; I shbiv a moth atip'nof the trunk circuit of iny invhtihn, the said tr'unk being p'rb'vild With a rfieatihgcdil.

Fbi' fa mpre complete unizlei'standing of my invention, referencem'y be had it: the :iceompanying drawings in' ivhi'c'h only snffic entiipparalZus is shown fdi' Connecting a calling snbs'crib'er at the iniiin' k'c'haiig' with :1 called subsc'r'ilier at 21' private biiineh e15:- change, A c'o'nnectin is cdnipl'ted thi'ough the medium. of the s'ubsci-iliers line? iqu'i 'iment L iiin exehange ctn'tl circ uit C, thrill; vnemt prwat' ln'smeh ex'chang'g'e cnrtleif cnit E, and the line eqnipinnt ll n'f the railed sulis'srrihr. j

Refeii'in'g m n't-m'e in detail tn the zippur'utus as illustrated in Fig. 1; I sh'oiv a hailing snhStatin-n A if any won ltrinwn msuitub'lt: type, of (ninmon miner; .'-:uh.=:t:ili(m which terminates in a line circuit ll. (r-tnhprising the usual line relay LR. line lash fcnt-ofi' relay CO. and the multiple jacks J. The cord circuit may be of any suituhle 01' well known type, and as shown (mnii'ises a answering plug AP .llll'l :1 cal ng plug CI connected by the heavily l'llfllhftl conductors a'nrl having the condensers K and K interposed. Assncizited with the answering plug AP is the answering tip superfisnry relay AT and an answering sleeve snperhism'y relay AS. The two super ir=r r relays XI and i9 mntrnl the {'li(lill if thrmnu'ez'ing supervisory lamp All vhztm! with the m lling plug (P is flumlinf: ti}; supervisory relu ("l and the --.=1"

to the conductors of plug CP. The link circuit C is adapted to complete connections between local substations or for extending a call from a local substation over the trunk circuit D to a subscriber at a private branch exchange, or for completing a call initiated by a private branch exchange subscriber to a subscriber terminating at the main exchange.

The trunk circuit D terminates in a trunk jack TJ at the operators position in the main exchange, and in a jack J at the op erators board 'at theprivate branch exchan e, ";Asso,ciated with the trunk jack TJ is a fiine'relay LR, line signal S, and a cut-oif relay CO. -The line relay LR'and the, lihe signals are used when connections are extendedjfrom the private branch exchangeto the main exchange. Associated with the'opposite' end of the trunk circuit D is a link control relay LC and an alternating current relay'AC. The relays LC and AC have their armatures mechanically related to each other andco-operate with each other. The saidrelay AC is provided with a lock ing latch which upon the energization of marshy VAC locks'its'armature 12 in its operated position. jThejrelay LC is rovided with a cohi'iecting'link, which lin upon the energizationof t e relay LC engages the latch associatedfiwith the relay AC to restore the arnitue l EZ f AC to its normal position. ,QThJgirifiamm 15 of relay AC is free to move back and forth. A trunk signal TS is also provided, and the lighting of the said lamp notifies the rivate branch exchange operator that a ca 1 has been extended to the said private branch exchange from the, main'exchange. A locking relay LO, a super isory relay SR, and a recall relay RA are also provided for the said trunk circuit C.

The private branch exchange operators link circuit E comprises an answering plug AP and a calling plug CP, connected through the medium of the heavily marked conductors. An answering supervisory relay SR is associated with the. answering plug AP, the said relay controllin the an swerin supervisory lamp AL. A calling supervisory relay SR is associated with the callin plug CP', the said rela controlling the ca lin supervisory lamp C A listen ing key LK' is also provided and connects the private branch exchange operators set 0 to the cord conductors. A ringing key BK is provided which, when actuated. coir meets the ringing generator G to signal the called for private branch exchange subscriber. The private branch exchange substation is s milar to that of the main subscribers substation A and terminates in a line circuit L comprising a line relay LR line signal S and its associated jack J The circuit as illustrated in Fig. 2 shows a calling subscribers substation A terminating in a line circuit L comprisin the usual cut-off relay CO line relay LRflfline signal S and multiple jacks J. The main exchange operators cord circuit C comprises the usual answering plug AP and the calling plug Cl connected by the heavily marked conductors. The answering end of the cord circuit is provided with a local sleeve relaiy LS and an answering supervisory relay SR. The answering supervisory signal AL at the answering end of the cord circuit is controlled by the two relays LS and ASH. The calling end of the cord circuit is provided with a local sleeve relay LS and a calling supervisor relay CAL. A calling supervisory lamp C 2 is rovided and is controlled by the two relays AL and LS. A listening key LK is also associated with the cord circuit C, and when actuated connects the operators set 0 to the cord conductors. A fringing key RKZ, is also shown, which, when actuated, connects the rigging generator G to the calling plug The trunk circuit D terminates in jacks TJ at the operators positions in themain exchange, and in a jack J in the operators board at the private branch exchan e. The usual line relay LR, cut-off relay 0*, and the trunk si nal S are associated with the trunk jack TJ. The opposite end of the trunk circuit D is provided with apparatus similar to that just described in connection with Fig. l. The trunk circuit D as illustrated in Fig. 2 is provided with a repeating coil RC. Private branch exchange operators circuit E, private branch exchange substation B', and line circuit L are provided with apparatus similar to that described in connection with Fi 1.

Having described in general the apparatus employed in the embodiment of my invention as herein illustrated, a connection from a calling to a called subscriber will now be described 1n detail. Referring to Fig. 1, assuming that the subscriber at the substation A desires to initiate a call, upon removing his receiver from the switchhook, a circuit is closed through the line relay LR. The said line relay LR upon energizing, closes a circuitthrough the line lamp S. The operator upon noting'the lighted signal S inserts the answering plug AP of the cord circuit C into the jack J of the calling line, thus closing a series circuit through the air snoring sleeve supervisory relay AS of the cord circuit C and cut-oil relay C0 of line circuit L. The circuit extends from battery through the winding of the said answering sleeve supervisory relay AS sleeve contacts of the connected plug AP and jack J, thinlugh the Winding of the cut-off relay CO to ground. The cutoff relay CO upon energizatiou disconnects the line relay LR privatep ran'chexchange; the *o erator' n'ow from the subscribers line and completes the connectionl between the :conductors of the jack J and the subscribers li'rne, thus closing the. circuit through-to' the ans'wering tip supervisory relay'AT. The circuit through theanswering tip su eruisory' relay AT iexH tends fronr battery tiirough the winding of the; irelay AS; sleeve contacts of the connected plug AB and-jack d, alternate' com tact z of relay GO," through the substation A1, alternate cpntliiit 3"8-relay-"CO, tip con tactsrofi the ccifdected an'd plug AP, aindbthroiigh; the! wiindi-n of tlIQ tIp supervisory relay AT to groun Relay AT; upon energizingqpneventsithevprelnaturedi hting orfsrthe answrin supery1sory= l'amp 5L by the-:opefring contact- 4. The operator now; 'operatsilieritlistening key 1 LK to confiectashercoperaiior s 'sefi to; the cord "conductors 'andlcinguires the wants "of the callin isubscribeni n 1" l ponrlearningthat theicalliflg subscriber desires,;ieonnecticn.with1a subscriber at the callin GR'Flintdt'lie ijaek hTJ; a series cner circuits is-establislied through the cut ioffvay (301; asso'ciated'with' the jack -TJ and the calling"'slee v e superyisoryrelay plugTGRahd jacki EDJ and ithe-winding of thdicut-ofimehy 0071-130 ground, The cutoff relay- GGEg'm onwenergizing, disconnects theglinearelay li i'ifi-omrthe conductors of thetnunlu circuit D,;and'connects the'ti-p and sleere-conductorsiofi therlj aclc 'I J tot-he heavily-marked trunlsconductors "5 and-6; The

closing of-alternatelcontact 39 of relay vloses va circuit fori'the" calling supervisory lamp- CL.-from battery through the lamp CL and alternate. contact 39 to ground at normal contact 3001 relay CT. The said lamp vCL remains-1 lighted'until the rivate branch ear-change operator answers t 1e call. I he operator at the main exchange now actuatcsthe'ringing. key RIC bo'connect ringing current from the generator G to the trunk circuit Di The path for ringing current extends from the unground'ed pole of the generator G through the alternate contact of ringing key RK, tip contacts of the plug'CP and jack TJ, trunk conductor (3, normal contact 7' of the night jack NJ, conductor 8, through the winding of thealternatingr current relay AC, conductor 9, normal contact 10 of the night jack NJ. trunk conductor 5. alternate contact 11 of relay CO. sleeve contacts of the connected jack TJ and plug: (Ii through the alternate contacts of ringin; key RK to battery, and hzrk 20 the grounded pole of generator G. The alternating current relay AC, when energized by the said ringing current, attracts its armature 12, and the attraction of armature 12 allows the latch spring 13 to assume its alternate position. The spring'13 is provided with a hooked end which engages the armature 12 and locks the said armature 12 in an actuated position. The spring 13 moving to its alternate position, establishes an energizingcircuit for the trunk signal'TS, the said circuit being traced from battery through-the said lamp TS and to gro'undat alternatelatch spring contact 13. The'closing of alternat contact 15 of the relay AC upon the energization of the said relay is only incidental at this time and does not bring about any circuit chan es. The contact 15 is not associated with the latch sprin 13 and is moved to its alternate position an restored again when the relay AC is energized and de-energized.

The operator at the private branch exchange upon noting the lighted trunk signal TS inserts the answering plugAP' of the private branch exchange link circuit E into the jack J'.;-' However, if ringing current is being applied to the'trunlrconductorsof the trunk circuit-D, the alternatingcurrent relay AC will'rema'in energized 'as long as cur-' rent is being applied to the trunk circuit over the herein-before described circuit. Should the operator insert the answering plug AP into the jack J while ringingcurrent is thus being applied; the alternating current relay causes its spring 15 to move toits alternate position, opening the normal 10!) contact 15, thus preventing the link control relay LC from energizing, and due to the link control relay remaining at normal, the trunk conductors are interrupted at contacts 16 and 17, thus preventing the ringing current from 106 being transmitted to the operators set 0.

As soon, however, as the relay ."iC tie-energizes, it allows'its normal contact 15 to restore to close in. energizing circuit for the link control relay LC which may be traced 110 from battery through the winding of the said relay, conductor 18. norl'nal contact 19 of relay RE, conductor 20, normal contact 15 of relay AC, conductor 21, to ground at the now closed jack contacts 22 and 23, the said contacts being closed upon the insertion of the plug AP into the jack J.

The closing of the alternate contacts 16 and 17 of the relay LC establishes an cner- {Iizing circuit for the supervisory relay RR. the said circuitl cing traced frmn battery through th Winding ilnrein (T of the main exchange. link circuit C'.v normal mutact of th ringing lccv RK. sleeve contacts of the connected phi! Cl and incl; TJ. ultcruatc contact 11 of the cut-oil relay F" trunk conductor 5. alternate context l? of relay LC. conductor 2-5, winding of the relay' SR, conductor 26, normal Contact 27 of ielay TAO condu tor 2 al ernate contact 16.0f relay LC, trunk conductor (3, tip r011- tacts of the connected plug CT and trunk jack TJ, normal contact of the ringing key RK, through the winding of the relay CT, to ground. The relay CT, upon energizing, opens its normal contact 30 to efiace the calling supervisory signal CL of the cord circuit C, thus notifyin the operator at the main exchange that the private branch ex change operator has answered the call. The closin of alternate contact 31 of relay SR establishes an energizing circuit for the relay LO, traced from battery through the winding of the said relay L0, and conductor 32, to ground at alternate contact 31. The relay LC being energized as described, its

alternate contact 33 is closed, and upon the energization ofthe relay LO, its alternate contact 34 is closed, thus establishing a locking circuit forrela LO traced from battery through the winding of the relay L0 and its alternate contact 34, to round at alternate contact 33 of the relay 0'. The relay LC, upon energizing,causes the link 35 associated with the latch spring 13 to engagejhe same and raise the said spring 13 so that its hooked end disengages the said armature 12, allowing the said relay armature 12 to restore to normal. At the same time contact 13 is removed from its alternate contact, efi'acing the trunk si nal TS. The opening of.normal contact 21 of relay LO opens the initial energizing path for the relay SR, but, due to the fact that the relay SR energizes before relay LO does, its alternate contact 36 is closed before the normal contact 27 of relay L0 is opened. The substitute energizing path through the relay SR may be traced from battery through the relay CS over the before-traced circuit, through the winding of the said relay SR. through the now closed contact 36 of said relay SR, and conductor 28, to ground over the previously traced path.

Upon the insertion of the plug AP into the jack J, an energizing circuit for the answering supervisory lamp AL is momentarily established, traced from battery through the said lamp AL, normal Contact 37 of relay SR, and the sleeve contacts of the connected plug and jack, to ground at normal contact 31. Upon the energization of the relay SR, its normal contact 31 is opened, preventing the premature lighting of the said supervisory signal AL. The operator at the link circuit E now actuates the listening key LK to connect her operators set 0 to the trunk conductors, through the medium of the answering plug AP and jack J, and inquires the wants of the calling subscriber A. The private branch exchange subscriber B being wanted, the private branch exchange operator inserts the calling plug UP into the jack .l of the called line, closing the circuit of the supervisory signal CL, over a circuit traced from battery through the lamp CL, normal contact 40 of relay SR and sleeve contacts of the plug CP' and jack J, to ground at the sleeve of the jack. The said lamp CL remains li hted until the called subscriber answers. pon the insertion of the plug CP into the jack J the normal contacts of the jack J are opened to disconnect the substation control of the line relay LE The operator now actuates the ringing ke BK to connect ringing current to the call bell at the called substation B.

Upon the response of the subscriber at the called substation B, an energizing circuit for the supervisory relay SR is established, traced from batter through the lower Winding of the relay bit, the ring contacts of the plug C1" and jack J through the now closed contacts of the substation switch hook, back throughthe tip contacts of the jack J 2 and the plug GP, and through the upper winding of the relay SR fto ground.

The relay SR, upon energizing, opens its normal contact 40, effacing the calling supervisory signal CL. The callin substation A and the called substation l3 are now in conversational circuit, over the heavily marked conductors.

Assuming that the conversation has now terminated, the calling subscriber upon replacing his receiver opens the circuit of the answering tip supervisory relay AT of the link circuit C, and therebv allows the same to restore to normal. The answering tip supervisory relay AT, upon deenergizing, closes a circuit for the answering supervisory lamp AL at its contact 4. The called subscriber at the private branch enchangc, upon replacing his receiver, 0 ens the circuit of the supervisory relay S 2 of the link circuit E, thereby allowing the said relay SR to de-energize. The calling supervisory relay SR upon de-energizing, closes a circuit through the calling supervisory lamp CL at its contact 40, thus indicating to the operator of the private branch exchange that the called subscriber has replaced his receiver.

Assuming that the operator at the main exchange in response to the disconnect signal AL first removes the plu CP from the trunk jack TJ, the removal or the said plug from the jack brings about the de-energization of the relays CT, CS and CO. The apparatus of the cord circuit C and line circuit L are now at normal and available for use in establishing other local connections.

The removal of the plug GP from the jack TJ also allows the relay SE of the trunk circuit D to de-energize and close its contact 31. The closing of normal contact 31 of the relay SR again closes a circuit for the answering supervisory lamp AL of the link circuit E. The operator at the'private branch exchan e noting the two lighted si nals AL and EL withdraws theplu s A5 and CP' from their respective jacks and J The withdrawal-of the plug AP 'from the jackJ allowstheiijack springs 22 and 23 to open, bringing about the de energization of the link control relay LC. The link control relay LC upon tie-energizing, opens its alternate contact '33, opening the locking circuit-of the relay LO, permitt'n the said relay L0 to restoreto'nornialas-"l he supervisory lamps ALwand'CL are'pfl'aced due to the disconnection of the' answeri plug AP and-the calling plug'cP, and lihe apparatus at the trunk circuit D is restored to normal as-is also that of the link circuit E, and the link. circuit.-E is now available for establishing other rconnections at the private branch-"exchange. '4;- 4

Assuming. that the private branch exchange operator is the' first-to withdraw the plug AP from the jack J this withdrawal nsthe closed contacts 22 a11d23 to bring o a out'the de-energization 0f the link control relay- LC. *The opening of alternate contacts "16 and .17. of the saidielay LC brin about the de energization of the relay R, and-the opening of alternate contact 33 opens the locking circuit of the relay LO, allowing the said relay to restore to normal. The circuit of the calhn ti supervisory relay CT of'the linkecircuit at the main exchange de-energizes u on the restoration of the link control relay 01 the trunk B, to close a circuit for the calling supervisory lamp CL at its home! contact 30 to light the said lamp. The operator at-the link circuit. 0 now withdraws the answering plug AP and the calling plug '01? from their respective jacks J and TJ, and the relay (IO ofthe line circuit L'and the relay CO associated with the trunk circuit D restore to normal. The answeringsupervisory relay AS and the calling supervisory relay also restore, eifacing said signals AL and CL. The apparatus is now at normal and available for other connections. The removal of the plug CP from the jack J at the private branch exchange brings about the restoration of the apparatus at the link circuit A. as before described. It is thus seen that should the main exchange operator he the first to remove her plug CP from the trunk jack TJ. the restoration of relay SR of the trunk circuit D brings about the lighting of the supervisory lamp AL of the m'irate bninch exchange cord E. Should the private branch exchange operator be the first to withdraw her plug AP from the jack J. the restoration of the relay Lt as already described brings about the lighting of the supervisor} lamp CL of the main exchange link circuit C, this'lighting or" the supervisory l mps in the cords at the op at contact 23 91' the jack J, allowing the 13" posite ends of the trunk D depending on which operator was first to disconnect, thereby providing double supervision.

Assuming now that the calling subscriber A and the called subscriber B have replaced their receivers upon their respective switch hooks and the operator at the main exchange in response to the disconnect signal removes the plug CP from the trunk jack TJ, the relay SR of the trunk circuit D restores to normal, as previously described. Now, should the private branch exchange operator neglect to remove the answering plug AP from the jack J of the trunk circuit D, the plug AP remaining in said jack J" does not tie up the trunk circuit D. When a condition of this kind arises, the relays LC and LO remain energized due to the closed contacts 22 and 23 of the jack J, which closed contacts hold LC energized and the said relay LC in turn keeps the relay L0 in its locked energized position. The relay SR has its energizing circuit opened at contact 27 of relay L0 and, therefore, relay LR of jack TJ remains at normal, no-busy indication being given at trunk jack TJ. The main exchange operator may again insert the calling plug CP into the jack TJ and actuate her ringing key RK to connect ringing current from the ringing generator G to the trunk conductors. The ringing current will pass through the alternating current relay AC aspreriously described, and effect the closure of its alternate contact 13 to again light the trunk signal TS. Upon the actuation of the relay AC, due to ringing current passing through its energizing windin its alternate contact 15 is closed, opening the energizing circuit of the relay LC. The relay LC upon fie-energizing, restores and opens its alternate contact 33, thereby opening, the locking circuit f the relay LO. The relay LO being a slow-acting relay, that is. being slow to release i s armature. holds its contact in) momentarily closed after the de-encrgization of the said relay LC. and this act closes an energizing circuit for the recall relay RE. traced from battery through the winding of the said re lay. closed contact 50 of the relay LO. conductor 51. alternate Contact 15 of the relay AC and conductor 21. to ground at the contact 23 of the jack J. The relay RE thereupon closcs a lOCklDfl circuit for itself traced from battery through the winding of said relay RE. its alternate contact 52.-

ccnductor 53. and conductor 21 to ground at contact 23. The reli -hting of the trunk signal TS notifies the operator at the private branch exchange of the recall. The private branch exchange operator to place herself in communication with the calling subscriber withdraws the plug AP from the jack J, opening the locking circuit for the relay RE said relay to'restore to :nolmal. Then upon there-insertion of the plug Al? into the jaidc J, an energizing circuit for the .relay LC is established, which energizes relay LG and causes the energization of' the relay SR over the trunk conductors. The relay L0 is again energized to close a. locking circuit for itself, and the energizationof relay LC restores the. spring- 13 ofrelay AC to efi'ace the trunk signal TS, allof which has been previously described 5 in connection with the call from the calling subscriber'A to the called subscribertB. The operator .at the private branch exchange cord Enowlactuates hQ/IfIlStGIIlHgekeK IJ K' .to connect he'r operators' set O t0.-;the trunk conductors through the medium "oi; the plug AP and jack J to inquire the wants-of the. calling subscriber A. a, I

It will thus be s een thafiwhen the main exchange bperatorire-rings over a-trunk on whichthe prirateibranch exchangeoperator has left it-he plugs inflthe jack -5 ringing; current: is. cutf ofi horn-the. .rivate' branchexchange board (due bathe re ay LC de-energiz ing upon the'iwtuatiomof-the alternating current relay AG,-.3vhich relay AC opens its normal contapt15 to bring allout-the deenergizationofthef saidlrelay-LC. The relay LC restoring opens its alternate tftllltil-Cl-S 16 and17, open'hn ,he :trunkcoiulnctcrs of; thetrunkcircuit D, preventing the ringing current from passing to theprivate branch exchange cord E and ringing the operator in the ear,'shoulL-her.listening kevLK be actuated, andpmventingthe ringing of the private branch-exchange subscribers call boll should the plug GP remain in the jack-I. Y: I 1

Assuming now that a subscriber at a private branch exchange wishes to communicute with a subscriber at the main exchange, the subscriber at the private branch exchange upon removing his receiver brings about the energization of the line relay LR from battery through the said relay. normal contact of jack J, through the substation to ground at the jack spring of the jack J". Upon the energization of the relay LR", the line signal S is lighted. The private branch exchange operator now inserts the answering plug AP into the jack 3 of the calling subscriber, and this insertion of plug AP opens the normal spring jack contacts of the jack J 2 to bring about the de-energization of the line relay LR and the etlar ihent of the line signal S. The relay Sl-i' of the link E is also energized m or the line. preventing the light ng of the supervisory signal AL in a well known manner. The operator now actuates the listening key LK to inquire the wants of the calling subscriber, and upon learning that the wanted subscribers line terminates at the main exchange, she inserts the calling plug OP into the jack J of the trunk circuit D, bringing about the lighting of the calling supervisory lamp CL, over a circuit traced from battery through the said lamp, normal contact 40 of'relay SR2 sleeve contacts of the connected plug GP and jack J to ground at normal contact 31 of relay Sit of the trunk D, the said lamp CL remaining lighted until the main exchange operator answers the call. The insertion of the plug AP into the jack J closes an energizing circuit for the link control relay LC traced from battery througl .the winding of the said relay LC, conductor 18, normal contact 19, con' ductor 20, normal contact 15, and conductor 21, to ground at closed contacts 22 and '23. The closing of alternate contacts 16 and 17 of the relayLC extends the trunk conductors to the trunk jacks TJ at the main exchange. The line relayLR at the main exchange is energized over a circuit traced from battery through the winding of the said relay, conductor 6].,-normal contact-60 of relay CO, trunk: conductor 6, alternate contact 16 of relay LC, conductor 28, contact 27 ofrelay LO, conductor 26,through the winding of the relay SR, conductor 25, alternate contact 17 of relay LC, trunk conduct/or 5, to ground at normal contact 11 of relay CO. The relay SR of the trunk circuit D is not'cncrgized through the line relay LR, due to thehigh resistance of the relay LR, ulid remains at normal. The closing of alternate contact 62 of relay LR brings about the lighting of the line sig- 100 mil S.

The operator at the main exchange now noting the lighted signal S inserts the answering 'plng AP into the trunk jack TJ, establishing a series energiz'ng circuit for the relay AS and cut-off relay CO over a circuit traced from battery through the winding of the relay AS, sleeve contacts of the connected plug and jack. and through the winding of the relay (0' to ground. The opening of nlternalc contact ll. upon the energizutiou of the relay C0. brings about the restoration of the line relay LR to cllucc the line signal S. A circuit for the rule) .'l f the main exchange l nk cir- H5 unit 7' and the relay b ll of the trunk circuit D is now established traced tron! buttery through the winding of the relay AS, sleeve contacts oi the connected plug and jack, alternate contact ll of relay CC" trunk coir ductor 5i. alternate contact 'IVT. conductor .35. winding of the relay SR1 conductor 36. nor llllll contact 37. icondlutlor l3. alternate row tin-l H9. trunk ronductor (3. contacts of the connected plug and jack, through the \riinl- 13!, in; of the relay AT to ground. Normal contact 4 of relay AT is opened, preventing the supervisory lamp All from lighting. Upon the energization of the relay SR, its normal contact 31 is opened, interrupting the r u t f t supe isory huepC of the private branch exchange link E, notifying 1 .16 .QPrfitor t th aid branch exchange that the main exchange operator has answered the call. The dosing of alternate contact 31 of. the releySR establishes an energizing circuit. for h r lay L9, a the closingof alternate contact-.34 of relay LO eStQbIiShes s lookingcircuit ,for itself, as pr vicn lyg fieri ed- The operator at the min 'elgehange now actua esher-li t keyfLK to connect-her operators 's'li Qfani inquires the wants of the calling, subscriber; Assuming that it is the main eis'hal gs subscriber A that is Wanted, she inserts the. plug C1 into the 539k. a d etes h r rms gfk y to r ng the bell of theinu led subscriber A. U992 t e-insertlou 1 gl P nt h 113431?? :91 3) Gotrhe Aind the cutefifielnr-g, LQ. ,ere.;energ{ edr: s e and q i i l t i w ieg ises -PlfiP ii f RQ qll fllll' l. a 1 .C; M1 notify ng "Lefiasji" h -$1 J1 he o 's'retb iiitli i .mpi i. wh n the-1 w e11... .s'uhser beir iesien uet dg .Tlwf s11] s'c'ri rs ih'ay new-cam, ans erer-i611. over the; E heav ly marked e nin -tars. .lrThe (liscoenbct on' f he paratu in es bl s a cgnnectibn f ro xn"the; private branch oxchnnge; sgbscr 'ber to}; Hui-in exchange ub criber. 1 inl1.i1. r, ,0 h t pr v sly descriheglj' 1 1. .F 2,. I illns imte a' tr nk circuit D hati g e tr s operation a .thatd S r n cons nts; lthlFiil, but n ad I show e'rep eeti ng coil. fi-Qizgs cinted with the r k cirrultl); .N wfle m g ha the ubsc iber a t e .-$ub$ tion A i t a cull, upon"renjovingfhis'receiver from the switch hook mcircmt isclqsed through the line relay LR, which'relay upon energizing closes a circuit through the line signal 8*. The main exchange operator noting the lighted signal S insertsthe answering plug All into the jack J of the calling line. The series circuit is established for the cutoff relay CO and the local sleeve relay LS of the cord circuit C from battery through the winding of the relay LS, sleeve contacts of the connected plug and jack, through the winding of the relay CO" to ground. The supervisory relay is also operated over the line conductors upon the energization of relay CO", end the energization of the said relay AL brings about the opening of its normal contact 80, preventing the premalure li hting of the answering supervisory relay XL, The operator now uctuates her listening key LKQ to connert her operators set 0" to the cord conductors, and inquires the wants of the calling subscriber. Upon learning that the calling subscriber desires connection with a subscriber at the private branch smhenge, the opera-tor now inserts sj bscriber,

the calling plug GP into the trunk jack TJ'. establishing u series energizi circuit for the local sleeve relay LS, an cut-ofi' relay CU, traced from battery through the relay LS, sleeve contacts of the plug and jack, and through the winding vofthe cutoff relay CO to ground. The cut-ofi' relay CO upon energizing disconnects the line relay LR frpm the conductors of the trunk c'ircuitD' and connects the tip and sleeve nductors of the jack TJ to the heavily marked trunk conductors 5 and 6'- The closing of alternate contact 81 of relay LS otthe cord circuit C closes the circuit through the calling supervisory lamp CL, the said lamp remaining lighted until a privatebranch exchange operator answers the call. lThe main exchan e operator now actuates her ringing key RI 2 to connect ringing currentfrom the generator G to the trunk circuit D. The path for ringing current extends from the ungrounded .pole of the generator, G through. tip contacts oil *the connected plug and. jack trunk conductor 6, normal content 7' of the night jack NJ, the winding 82v of the repeating coil RC, conductor 8', through the w-inclingof-the alternating current relay AC, conductor 9, the winding 83 of the' repeuting'coil RC, contact 10' of the night jack NJ. trunk conduetor ,5, contacts of the connected plug and jack. through the alternate contactof the ringing key RK to battery, and'ba'clr to the grounded pole of the generator x The relay AC is also provided for the latch spring 13'. armature 12' and spring 15',.as described in .detail in the description of Fig. l. The closing of alternate contact 13" brings about the lighting of the trunk lamp Th.

The prirzrte -l)runcl1 exchange operator noting the lighted signal TS inserts the answering plug Al of the private branch exchange link circuit D into the jack J. However. if ringing current is being zip-- plied to the trunk conductors of the trunk circuit D. the alternating current relay AC will remain energized as long us current is being applied, and should the operator inn-:urt the answering plug .\l into the lurk 'l \rlzilc ringing current is thus-dicing: upplieul. the normal cunt-Act 15' of the alternating current relu .Ul" is in its ulteriratc jiosition. preventing the uno 'g nz l-i-an of" the l nk. roulrul relay" ll". thus preventng: the suit] ringing: current from being isrxnvxnflled lo lllf? operators set U". As soon :is relay A C is dwenergizrrl after ringim: iurri-zil. has been discontinued. cunt-art as umes ils nurmul position and the plug KP in the jack J. :1 circuit is closed For the snid relax LC traced from batter through the winding of the relay LU, conductor 18, normal contact 19 conductor 20. normal contact 15, conductor 21', to ground at spring jack contacts 23 and 22. The closing of alternate contact 84 of relay LC establishes an energizing circuit for the supervisory relay SR of the trunk circuit T), traced from battery through the lower winding of the supervisory relay CAL of the main exchange link circuit C, through the contacts of the connected plug (P and trunk jack TJ', conductor 5', normal contact 10, winding 83 of the repeating coil RC, conductor 85, winding of the relay SR conductor 26', normal contact 27', conductor 28, alternate contact 86 of relay LC, conductor 87, winding 82 of repeating coil RC, normal contact 7, trunk conductor 6', tip contacts of the connected plug CP and the trunk jack TJ through the upper winding of the relay CAL to ground. The operation of the apparatus of the trunk circuit D as to the efi'acernent of the trunk signal TS, due to the energization of the relay LC, and the energizing of the locking relay L0 and its looking circuit is the same as has been previously'described in connection with Fig, 1, and a; further description is not necessary. The connection which is extended to the called,private branch exchange B is practically the same as described in detail in Fig. 1, and the features of double supervision and the provision of means for allowing the main exchange operator to re-ring over a trunk upon which the private branch exchange cord circuit is still connected is the same as that described in connection with Fig. 1. Disconnection of the apparatus used inestablishing a connection, and the calling of a main exchange subscriberby a private branch exchange is the same as previously described in connection with Fig. 1.

While I have illustrated the preferred embodiment of my invention in certain specific circuit arrangements, yet itis to be understood that I do not wish to be limited to the arrangements as shown as many changes and modifications will readily suggest themselves to one skilled in the art, and I, there fore. desire to cover all such changes and modifications as come within the spirit and scope of the appended claims.

What I claim as new and desire to secure by United States Letters Patent is:

1. A telephone system including a calling and :1 called subscribers line. u cord circuit, a trunk circuit provided with a pair of terminals. and a second cord circuit connecting said lilies in. conversational circuit. means for preventing the connection of one of said terminals to said trunk circuit while signalling current is being applied to said trunk circuit. a supervisory signal for each of said cord circuits, means whereby when either of said cord circuits is disconnected from said trunk circuit the supervisory signal of the other of said cord circuits will be ef fected, and recall means for said trunk circuit operable to denote a recall prior to the disconnection of said second cord circuit from said trunk circuit.

2. A telephone system including a calling subscribers line, a cord circuit for connection thereto, a supervisory signal for said 'cord circuit, a called subscribers line, a cord circuit for connection thereto, a supervisory signal for said latter cord circuit, a trunk circuit for use in extending connection from said first cord circuit. to said second cord cir cuit, means for preventing the effective con nection of said second cord circuitto said first cord circuit while signalling'current is connected to said trunk circuit, means where by the disconnection of either of saidcord circuits from said trunk circuits will operate the supervisory signal at the other of said' cord circuits, and a supervisory signal for said trunk circuit operable to indicate, a call prior to the connection of said second link circuit to the said trunk circuit and also '0 erable to indicate a recall prior to the dls connection of said second link circuit from said trunk circuit. V r

3. A telephone system includinga calling and a called subscribers line, a link circuit associated with. each of said subscribers lines, a supervisory signal for each of said link circuits, a trunk circuit for use in extending a call through one of said link circuits to the other of said link circuits, means for preventing the connection of one of said link circuits with the other as long as signalling current is connected to said trunk circuit, means whereby the disconnection of either of sziid link circuits from the said trunk circuit will operate the supervisory signal of the other of said link circuits,randa supervisory signal for said trunk circuit operable to indicate a call prior to the connection of said second link circuit to said trunk circuit and also operable to indicate a recall prior to the disconnection of said second link circuit from said trunk circuit.

4. A telephone system including a calling subscrihers telephone line and it called subscrihcrs telephone line, a link circuit, a trunk circuit and a second link circuit, all used for cxtendiiul a connection from said calling subscribcrs line to said called subscribers line, a supervisory signal for said second link circuit, means responsive to the disconnection oi said first link circuit from said trunk circuit for actuating said superrisory signal, and recall means for said trunk circuit operative to eii'ect a trunk signal to cause the same to burn continuously until the recall is answered when said second link circuit remains connected to said trunk circuit, and no matter in what condition said link circuit signal may be.

5. A telephone system including an A operators link circuit, a two-conductor trunk circuit provided with terminals, aB o'pera tors link circuit, means to prevent the operative connection of one of said terminals with the other of the terminals as long as a signal is being transmitted over said trunk circuit, a supervisory signal for said B-o erators link'circuit, means controlled by the A operator over'the conductors of the outgoing end of said trunk-circuit in series for operating said supervisory signal, and means for restoring said-supervisory si 'alY-i 6. A telephone system'including an A operators cord circuit, a B operators cord circuit, a trunk circuit for connecting said cord circuits, a supervisory signal for said B operators cord circuit, means controlled by said A operator for causingftheoperationof said supervisory "signal, a calling signal for said trunk circuit, and means controlledb the A operator for causin said calling sig'nal to glow continuously until the B operators cordcircuit is disconnected from the's'aid trunk circuit.

7. telephone system including an A operators cord circuit, a; B operators coi'd circuit, a trunk circuit connected to said cord circuits, a supervisory signal for said B operators cord circuit, means respon sive to the'disconnection of the A operator.s cord-circuitfrom the trunk circuit for causing the glowing ofsaid B 'operators supervisory's'ignal, a signal for said trunk circuit, and 'means controlledby the A operator for caus' a continuous operation of "said trunk circuit signal. to denote a recall until the B operator disconnects the B operators cordcircuit from the trunk circuit.

8; A telephone system including an A operators cord circuit, a B operators cord circuit, a trunk circuit for connecting said cord circuits, a supervisory signal for said B operators cord circuit, means controlled by the A operator for causing said supervisory signal to glow to denote disconnection, a supervisory signal for said trunk circuit controllable by the A operator when she signals for a recall,said signal being operative even though the B operators cord circuit remains in connection with the trunk circuit, and means controlled by the disconnection of the B operators cord circuit from the trunk circuit for eifacing the signal of said B operators cord circuit and for efi'acing said trunk circuit signal when the B operators cord circuit is again connected to said trunk circuit.

9. A telephone system including an A operators cord circuit and a B operators cord circuit, a trunk circuit provided with a pair of terminals for connecting said cord circuits, means for preventing connection to one of the terminals to the trunk circuit while a signal is being transmitted over the trunk circuit, a supervisory signal for said trunk circuit and a supervisory signal for said 'B oper'ators cord circuit, and means controlled by the A operator for efi'ecting both of said supervisory signals, said means adapted' tocause said trunk supervisory 'si nal' to gloW- continuously to denote a reca 1 until answered when said second link circuit remains'connected'to said trunk circuit.

10. A telephone system including an A operators'cord circuit and a B operators cord circuit, a thinkcircuit for connecting said ccr'd circuits, -a supervisoryfsignal for said trunk circuit, means for'preventing operative connectionof one of said cord circuits with said trunk circuit while signalling current'is being connected to said trunk circuit, anda' supervisoryfsignal forsaid B operators cord circuit, means-controlled by the A operator'forlactuating the supervisory signal of 'said B operatdris cord circuit to denote disconnection, means controlled by the A operator for' d'p'erating said trunk supervisoryfsignailto denote'a recall, and B-operato'rcoiitrolledmeans for" eflacing 'said trunk circuit signal. v

11'. A telephone system including an A operators cordcircuit and a B operators cord circuit, 'a trunk circuit for connecting said cord circuits, a supervisory signal for said trunk circuit, a supervisory si nal for said B-"operators*cord circuit, an means controlled by the A 'o perator for actuating bothfof said signals to denote a recall prior to a disconnectionofsaid B operators cord circuit from said-trunk'circuit. '7'

12. Adelepho'nesystemincluding an A opcrat'ors cord circuit and a B operators cord circuit, a trunk circuit for connecting saidco'rdcircuits, a supervisory signal asso-' ciated with each end of said trunk circuit, said signals beingindividualto said trunk circuit, means whereby the A operator may disconnect the A operators cord circuit from said trunk circuit without cfi'ecting the supervisory signal at the outgoing end of said trunk circuit, means whereby the A operator may effect a signal at the incoming end of the trunkcircuit to denote a recall prior to the disconnection of said .B op erators cord circuit from said trunk circuit, said recall signal continuin effective to denote a recall until answered even after the A operator has 1 ceased working said means.

13. A telephone system including an A. operators cord circuit and a B operators cord circuit, a trunk circuit for connecting said cord circuits, a supervisory signal associated With each end of said trunk circuit and individual thereto, and means whereby the A operator may disconnect the A operators cord circuit from said trunk circuit without. effecting the supervisory signal at the outgoing end of said trunk circuit prior SLO toa disconnection of said B o erators cord circuit from said trunk circuit and means whereby the FA? operator may efi'ect:the supervisory signal at the incomingend of thevtrunk circuit to denote a recall prior to a disconnection of said B operators cord circuit from said trunk circuit, said recall signal continuing efi'ective to denote a recall until answered even after the A operator has ceased working said means.

.14..A telephoneusystem including an A operators cord vcircuitiand a B operators cord circuit, a trunk circuitforconnecting said cord circuitsca supervisory signalassociated with each end of said trunk circuit, said .signals:being individual to the trunk circuit, means whereby the A operatormay disconnect the A o erators cord circuit from said trunk circuit Without effecting the supervisory signal at the outgoingend of said trunk circuitprior to a disconnection of saidEB operators cord .circuit from said trunk circuit, ineanswhereby the fAKoperator may eifect the. supervisory signalat the incoming end of saidv trunk circuit. prior to disconnection of said B. operators cord circuit from said trunk circuit to causethe said incoming end supervisory signal to glow continuously untilsaid .B operators cordis disconnected trom said trunk circuit, means "for disconnecting said B operators cord circuit .froui said trunk circuit, and means responsive to a reconnection of said B operators cord smu to. saidtrunk circuit to operate the-supervisory signal at the A end of the trunk circuit.

15. A telephone system including a calling subscribers line, a link circuit provided with .acsupervisory signal associated with said calling subscribers line, :1 called subscribersline, a link circuit provided with a supervisory signal associated with said called subscribers line, a trunk circuit for extending a call from said first link circuit to said second link circuit, and means rcsponsirc to the disconnection of said Iirst link circuit from said trunk circuit for operating the supervisory signal at said second link circuit, means responsive to the disconnection of said second link circuit from said trunk circuit for operating the supervisory signal of the said first link circuit, and a signal for said trunk circuit controllable by the A operator for denoting a recall prior to a disconnection of the B operators cord circuit from the trunk circuit.

16. A telephone system including a trunk circuit provided with terminals, one terminal of said trunk circuit being normally disconnected from the other terminal of said trunk circuit, means For connecting said terminals-together, means for applying signaling current to one end of said trunk circuit, and means associated with said trunk circuit for preventing the operation of said connecting means as long as signaling current is being applied to the saidtrunk circuit.

l7. A telephone system including a trunk circuit, terminals in whichssaid trunkcircuit terminates, oneof saidterminals being normally disconnected from said trunk circuit, connecting means for, connecting said terminal to said trunk oircuit a 'sourceof signaling current, means for connecting said source of current'to oneend-of said trunk circuit,. and. means i or prerenting the operation said connecting. means as long as the said source of currentis' connected to said trunk circuit. I

.18. A- telephone system including atrunk circuit .proyided WithTterminals; one of; said terminals being. normally disconnectedfrom the other of saidterminals, means ,res onsive ton. connection to one qt saidlteriiiinals for connecting saiditerminals together, and means for preventing, the connection of said tcrminalsitogether when said connection is made to one of said terminals. y

:19. .A telephone system includinga trunk circuit,provi'ded with apair of terminals, one of said terminals being normally disconnected irom said trunkcircuit, a link circuit means. responsive to the connection of said link circuit to said trunkicircuit to connect said normally disconnected tenminal to said trunk circuit, and, means "for prerenting the connection of said normally disconnected terminal to s'ai-dirunk circuit when said link circuit is connected to said trunk circuit. y

20. A telephone system including a pair of cord circuits and a trunk circuit connecting a pair otsubscrihers lines, a supervisory signal for said trunk circuit. asource of signaling current for one of said cord cir cuitsadapted to be connected to said trunk circuit to cause the operation of said trunk circuit signal, means responsive to the connection of said-other .tOILl circuit to said trunk circuit to elface said supervisory signal, means responsive to a second applica tion of said current to said trunk circuit to reoperate said trunk circuit signal, and means responsive to the disconnection and reconnection of said second cord circuit to said trunk circuit for again eii'ucing said trunk circuit signal.

Signed by me at Chicago, in the county of Cook and State of lllinois, this 2nd day of April, 1918.

CHARLES SPARKS.

lit] 

